Field of the Invention
The invention relates to a method of manufacturing a superconductive cable which is equipped with means for compensating for the length changes which are created when the cable is cooled from room temperature to work temperature and vice-versa, and wherein a superconductive cable is used with a tubular central carrier which is surrounded by at least one superconductive conductor, and wherein in the carrier is arranged over the entire length thereof at least one tension-proof strand.
Description of Related Art
Such a superconductive cable is disclosed in for example, U.S. 2010/0285968 A1.
A superconductive cable has electrical conductors of a material which changes over into the superconductive state at sufficiently low temperatures. The electrical direct current resistance of a correspondingly conductor is zero if sufficient cooling has been carried out, as long as a certain current, i.e. the critical current, is not exceeded. Suitable superconductive materials are, for example, oxidic materials on the basis of rare earths (ReBCO), particularly YBCO (yttrium-barium-copper oxide), or BSCCO (bismuth-strontium-calcium-copper oxide). Sufficiently low temperatures for bringing such a material into the superconductive state are for example, 67 K and 110 K. However, there are also superconductive materials, for example, magnesium boride which must be cooled to even lower temperatures if they are to change into the superconductive state. Suitable cooling agents for all these materials are for example, nitrogen, helium, neon, and hydrogen, or mixtures of these substances.
When operating an arrangement with at least one superconductive cable, the latter is arranged in accordance with conventional technology, in a cryostat which consists of at least one thermally insulated pipe and through which a cooling agent is conducted which is suitable for the superconductive material being used, i.e. a cooling agent mentioned above. For achieving the superconductive state within the cryostat the cable is significantly cooled so that it becomes shorter as a result of the thermal contraction. In order to ensure the operability of the length of transmission, requirements have to be met through which the shortening of the cable is compensated. in such a way that it does not have a harmful influence on the cryostat or the cable on the one hand, as well as on the cryostat or the units connected to the cryostat or the cable, on the other hand.
In accordance with the method of EP 1 720 176 B1, a superconductive cable is shaped at room temperature through a cross-like network of wires having tensile strength, for example, of invar steel and are connected to the cable in a dot-like manner in such a way that it extends in accordance with the shape of a wave. The superconductive cable is introduced in the respective wave-like shape into a cryostat composed of two concentrically arranged pipes between which a vacuum insulation is provided, through which a cooling agent is conducted during the operation of the appropriate arrangement. The cable which becomes shorter as it cools changes over into a stretched state without generating a mechanical load on the cryostat or the units connected thereto. This method can be carried out in practice, however, it is very complicated.
The above mentioned U.S. 2010/0285968 A1 describes a method by means of which the thermal contractions of a superconductive cable are to be compensated. The cable has a tubular carrier around which two superconductive conductors separated from each other by an insulating layer are arranged. A strand with tensile strength is arranged in the carrier which is secured after the placement of the cable at both ends thereof, for example, by means of clamps. The ends of the cable are compressed in the axial direction by means of the strand in such a way that the conductors, at their ends, have a wave-shaped configuration resulting from the respective shortening of the length.